I simply say "I like trains", causing a train to spontaneously appear and run over the potato, destroying it and the gun. (ASDF movie logic)

The next user is a normal human who got crushed to death by the same train.

Will be run over, not got run over.

I say "I like trains," causing a train to appear in another direction. The two trains collide and their sum velocity pushes them away from me.

The next person is bound and gagged in a chair in an open field, with a tape recorder constantly saying "I like trains."

i manage to cut through the ropes with my telekinetic abilities and dodge the trains (if that is what you were inferring).

the next user is stoned (or on drugs) and thinks that they are on fire, so they run to a pool and jump in. turns out the pool was a volcano.

"the pool was a volcano" it is not active. it is just like a lake.

the next user is trapped in a erupting volcano.

I quickly teleport to location just outside...

...the next user's house. where i poison there drinking water. 

however, you do that after i begin moving to another house.

the next user drinks a gallon of deadly poisonious water.

that goes through my poison filter before coming through my fosset and fridge.

How ever, the next user is trapped in a diamond room that prevents all escape methods including teleporttation and transporting, and then fills up with liquid nitrogen.

I shrink to the size of an electron and crawl out between the carbon atoms of the diamond before the liquid nitrogen reaches me.

the next person just swallowed thirty ghost chillies in the middle of a desert with nothing but sand for a thousand kilometers in every direction.

I had already processed the peppers, removing every trace of the capsaicin that gives them their dangerously hot flavor. As a result, nothing happens.

I force-feed the next user with a kilogram of powdered radium, leaving them to die of non-curable radiation poisoning, radiation burns, and cancer.

i lay there until somone with a time machine comes along. i stab them with a shiv, and go back in time to stop myself being fead radium.

while i am back in time i also nuke the next user's country before they are 10 years old.